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Executing a push cut correctly... (Read 676 times)
 
John Grace
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Executing a push cut correctly...
Nov 3rd, 2017 at 6:29pm
 
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In this video by Glenn Lucas he is executing a cut that I've been trying to emulate with mixed results.  The specific spot in the video begins at the 3:36 mark.

As a general rule, I've not had much trouble executing this technique on green/wet wood but have met with mixed results once the piece has completed drying.  Some of the questions I have include; is this a cut that's best done only on wet wood, is there a better shaped gouge than another for this technique, or is it simply a matter of mastering the cut?  On those rare occasions when I do get it right, the finish is impeccable with absolutely no tear-out.  Sadly...even when I do seem to get it right, I do so infrequently enough that I cannot ascertain what went right vs wrong.

Again, I've been successful on wet wood.  When I attempt it dry pieces, I can typically do well for an inch or so on the inside of the bowl but I'm really struggling either maintaining a flowing cut or the tool starts to chatter and bog down terribly.  And yes, the gouge is freshly sharpened and the tool rest is no more than a 1/4 inch from the piece.

I've even tried the technique in reverse...cutting on the 'opposite' side thinking that would give me a better angle of attack to the piece.

Unfortunately, due to either work hours or the demands on the home front visiting a turning club is impractical.
Any thoughts or specific videos would be much appreciated.

As always...thank you, John
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Don Stephan
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Re: Executing a push cut correctly...
Reply #1 - Nov 3rd, 2017 at 7:40pm
 
One possibility is coming off the bevel.  If the angle to the wood becomes ever so slightly steeper the tool will take a deeper cut.  If the angle becomes slightly less steep the cutting edge will begin to rise off the wood, making a shallower cut.  And if progressing along a changing radius, if the bevel is long the heel can press against the wood, which has the effect of lifting the cutting edge.  It seems illogical, but I have not seen the quality of cut diminish with a primary bevel as narrow as 3/32".

These are all the thoughts I have right now.
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Re: Executing a push cut correctly...
Reply #2 - Nov 4th, 2017 at 12:01pm
 
A few things come to mind,
While I don't turn green wood I do still make this type of cut as my final pass. I also have less than perfect results but much more positive than negative.
This is what I've found that works for me. YMMV

Tool handle length and diameter.
The longer the tool handle, the more control. It is easier to produce a smooth sweeping motion with a longer handle. (NOT opinion, Geometry/Physics)
The diameter of where you grip can also come into play for much of the same reasons as the length. A slightly fatter handle requires less grip or "clenching". This can result is less hand fatigue as well as a smoother rotation of the tool. (if you're trying to rotate by a degree at a time, it's easier to do with a fatter handle)
Cutting edge.
While my grind is different than the one in the video, I do employ a second and sometimes third relief bevel on the heel of the tool to prevent lift off and loosing the bevel.
Other than practicing that's all I can think of right now.
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Mike Mills
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Re: Executing a push cut correctly...
Reply #3 - Nov 4th, 2017 at 12:22pm
 
I am not a good one to reply but in my limited knowledge the following may also contribute to the problem.
In the video you linked to...
Note about 3:40 how light the left hand is on the tool, the cut is made with the right.  At about 4:00 note that he is cutting in steps, maybe an inch at the time leaving mass in the bottom to lessen vibration.  In Stuart Batty's videos he has two (at least) on Right Hand (steering) and Left Hand Braking.  Link to his videos below.
Are you slowing down the cut on the dry wood?  Are you riding the bevel or following the bevel?... too much pressure on the bevel may also set up vibration as it gets thinner.
In some of Lyle Jamieson's youtube videos he shows just how little pressure is needed with some cuts.  Lyle also has a video which shows what Don described in making thinner or thicker cuts.
Here is the link to Batty at Vimeo.
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John Grace
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Re: Executing a push cut correctly...
Reply #4 - Nov 4th, 2017 at 2:14pm
 
Thank you all for offering comments and suggestions.  I'll review all of them and the videos later this evening to compare against what I'm doing.  Cheers...John
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Don Stephan
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Re: Executing a push cut correctly...
Reply #5 - Nov 4th, 2017 at 7:30pm
 
Something I don't do often enough is move the tool with my body - much smoother than moving it with my arms.
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robert baccus
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Re: Executing a push cut correctly...
Reply #6 - Nov 4th, 2017 at 9:56pm
 
Try learning how to grind and use a bottom feeder gouge.  Makes the inside of bowls quite easy.
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John Grace
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Re: Executing a push cut correctly...
Reply #7 - Nov 4th, 2017 at 10:32pm
 
robert baccus wrote on Nov 4th, 2017 at 9:56pm:
Try learning how to grind and use a bottom feeder gouge


I've no problems along the bottom...it's along the inside walls of the bowl that are the primary issue.  Are you suggesting using a bottom feeder for the sidewalls as well???
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John Grace
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Re: Executing a push cut correctly...
Reply #8 - Nov 4th, 2017 at 10:54pm
 
Thanks everyone...I think you've all contributed to me having a better understanding of where my technique has been failing.  A little error here and there and it's easy to see where I've gotten off track.  I've found the Lyle Jamieson video, see below (thanks Mike).  While I picked up some excellent technique ideas from this video...his large scale drawings put some fundamental concepts of the push and pull cuts in their proper perspective.

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robo_hippy
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Re: Executing a push cut correctly...
Reply #9 - Nov 5th, 2017 at 12:14am
 
Well, this is a multi part question. Best bet would be to have a hands on lesson....

Some times it is the wood. Different woods will cut more cleanly or with more tear out. Pacific Madrone cuts like butter no matter what tool you use. I turned a piece of Koa that was air dried for 10 plus years, and I had to use the water method to clean up some of the most nasty tear out I had ever seen: get surface damp, let soak for a minute or two, then very gently, take tiny cuts and turn off the wet wood, repeat as necessary. It took at least 4 wettings to get it to some thing that was sandable.

Tool sharpness is huge. Most woods, a 180 grit edge (CBN wheel) is fine. On softer punky woods, or more stringy woods, then a 600 grit or finer edge works better, but that edge is lousy for roughing. Some times a hand honing will work.

For the inside walls, I prefer a 45/45 grind, hand done like Stuart's grind, but the 40/40 just doesn't feel right to me. In the transition and across the bottom, I prefer a 70 degree tool, and I have a number of different ones, but like Doug Thompson's fluteless gouge as much as anything else. I am fairly sure it was Stuart who commented that a 60 degree bevel takes more effort to push through the wood, and on some woods, for sure that seems to be true. On all the tools like that I have, I have more of a ) nose than a more pointed nose, and I am pretty sure the more broad nose had more resistance than the more pointed nose. I do tend to hold my tools level rather than the dropped handle method.

The one handed push cut is a good practice exercise. "The bevel should rub the wood, but the wood should not know it." No idea who said that, but love it. So, the handle hand, for most of us, the right hand, that is the steering wheel and the gas pedal. The left hand really does nothing other than rest on the tool. You need to push into the cut, and not onto the bevel. That causes all sorts of problems. How hard you push into the wood depends. For roughing, I am just trying to get rid of bulk, so they are not pretty, and I push just hard enough so that I don't stall my lathe, oh, I use scrapers, then I clean up with a gouge and finish with a shear scrape (that video coming out soon...).

You can't use a high speed rate in dry wood, you dull the edges, generate a lot more heat, and you get more tear out. This part is learning to 'feel' the cut. This depends on experience and personal sensitivity, but it does make different sounds in the same wood if you are pushing too hard, and more so if the tool is dull.

Catches come from many things. I think the most common are plunging the tool into a very uneven piece of wood and you get surprised. The other is a technique thing which usually involves coming off the bevel. This catch can happen either on the wing or the nose, with the wing probably being the more common. I always roll the flutes over on the sides, away from the wood, at 45 to 90 degrees. If You keep them kind of straight up, if you come off the bevel, you instantly have a point/edge sticking up into the spinning wood with no support.

I have a bunch of videos up on You Tube and in the video section here. Just search for robo hippy. Most of what I do is bowls.

robo hippy

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Ed Weber
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Re: Executing a push cut correctly...
Reply #10 - Nov 5th, 2017 at 10:57am
 
robo_hippy wrote on Nov 5th, 2017 at 12:14am:
You can't use a high speed rate in dry wood, you dull the edges, generate a lot more heat, and you get more tear out. This part is learning to 'feel' the cut. This depends on experience and personal sensitivity, but it does make different sounds in the same wood if you are pushing too hard, and more so if the tool is dull.

IMO, This can't be taught but must be learned by each individual. (trial & error)
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Re: Executing a push cut correctly...
Reply #11 - Nov 5th, 2017 at 5:36pm
 
Was watching some of the Stuart Batty videos this afternoon and they may at least clarify what type of resulting poor cut you are getting.  Search on Multimedia File Viewing and Clickable Links are available for Registered Members only!!  You need to Login or Register for Stuart Batty and watch in particular two videos he has labelled "Defects."

Dry wood is harder than green, and my experience is that it is harder to cut.
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John Grace
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Re: Executing a push cut correctly...
Reply #12 - Nov 6th, 2017 at 6:51pm
 
Ed Weber wrote on Nov 4th, 2017 at 12:01pm:
I do employ a second and sometimes third relief bevel on the heel of the tool to prevent lift off and loosing the bevel.


Ed...if you don't mind:
What angle do you use on your primary grind?
Are the second and tertiary grinds done free hand?
Have you experienced a better/worse outcome relative to the flute shape?

Again, thanks good friend...John
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John Grace
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Re: Executing a push cut correctly...
Reply #13 - Nov 6th, 2017 at 7:00pm
 
Robo...

robo_hippy wrote on Nov 5th, 2017 at 12:14am:
Most woods, a 180 grit edge (CBN wheel) is fine.


I use a 180 for my scrapers and a 320 for my gouges...I use your platform and I get better monthly.

robo_hippy wrote on Nov 5th, 2017 at 12:14am:
For the inside walls, I prefer a 45/45 grind


Can you better define what this means?  I set my platform at 45 and is the idea to 'sweep up' to the 45 degree mark?

robo_hippy wrote on Nov 5th, 2017 at 12:14am:
The bevel should rub the wood, but the wood should not know it


robo_hippy wrote on Nov 5th, 2017 at 12:14am:
"The bevel should rub the wood, but the wood should not know it."


When at my worst, I readily see the bruising when I rub the bevel too firmly against the side well.  Happens occasionally on the outside of the piece but mostly in the inside.

robo_hippy wrote on Nov 5th, 2017 at 12:14am:
plunging the tool into a very uneven piece of wood and you get surprised


I never attempt a push cut until the wood has been shaped to final contour with either my gouge or scraper...the choice of which is relative to the type of wood and the success on that piece to date.

robo_hippy wrote on Nov 5th, 2017 at 12:14am:
I have a bunch of videos up on You Tube and in the video section here.


And yes...I've watched every singe one of them at least once.  Any in particular you can suggest with this specific question?
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Ed Weber
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Re: Executing a push cut correctly...
Reply #14 - Nov 6th, 2017 at 7:57pm
 
John Grace wrote on Nov 6th, 2017 at 6:51pm:
Ed...if you don't mind:
What angle do you use on your primary grind?
Are the second and tertiary grinds done free hand?
Have you experienced a better/worse outcome relative to the flute shape?


Primary grind is somewhere in the 57-60 range.
Secondary grind is achieved by simply sliding the V-arm in towards the grinder about an inch and repeating.
I prefer a U flute for this cut. A V flute is too aggressive and seems to have a smaller sweet spot when sweeping through a long transitional cut.
JMO
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